Cucumber plants of the species Cucumis sativus belong to the cucurbit family, scientifically called the Cucurbitaceae. Within this family it belongs to the genus Cucumis, which does not only contain the important food crop cucumber, Cucumis sativus, but also a variety of melon types mainly included in Cucumis melo, as well as several other, less well-known species. It is an annual, herbaceous, flowering plant species which is thought to have originated in Asia.
Cucumber plants were domesticated early and have been cultivated for thousands of years in African and Asian countries. A wild progenitor of cucumber is found in Asia and taxonomically classified as a subspecies, Cucumis sativus ssp. hardwickii. The closest related other species within the genus is acknowledged to be Cucumis hystrix. Small Cucumis sativus types are used for pickling and are called gherkins or pickling cucumbers. However, varieties of Cucumis anguria are also small fruited and can be grown for the same purpose; they are usually called ‘bur cucumber’ or ‘West Indian cucumber’.
Cucumbers are presently cultivated worldwide in a large variety of types, which typically differ in size, color, and skin type. Cucumber fruits have a high water content and are therefore low in calories, but provide a source of various useful nutrients such as potassium, magnesium, calcium, and phosphorus, as well as vitamin C.
In 2012, the total acreage for fresh market cucumbers in the United States was approximately 19,150 hectares, with a total production of about 453 metric tons, representing a value of almost $248 million. Processing cucumbers or gherkins for pickles were harvested from 35,760 hectares which resulted in a production of about 448 metric tons, having a value of close to $172 million (source: USDA Vegetables 2012 Summary).
Cucumber production is most successful in a relatively warm climate and it prefers temperatures between about 18-25° C. Several pests and diseases can affect cucumber production, including several viruses that are often transferred by insects, but also bacterial and fungal diseases. Typical problems that might arise during cucumber production include downy mildew (Pseudoperonospora cubensis); powdery mildew (Golovinomyces cichoracearum and Podosphaera xanthii); Anthracnose (Colletotrichum orbiculare); Scab (Cladosporium cucumerinum); Angular leaf spot (Pseudomonas syringae pv. lachrymans); Belly rot (Rhizoctonia solani); Pythium fruit rot (Pythium spp.); the viruses Watermelon Mosaic Virus (WMV), Cucumber Vein Yellowing Virus (CVYV), Cucumber Mosaic Virus (CMV), Papaya Ringspot Virus (PRSV), Zucchini Yellow Mosaic Virus (ZYMV), Cucumber Green Mottle Mosaic Virus (CGMMV); and pest attacks by aphids, cucumber beetles, spider mites, and pickleworms.
Breeding for resistance against any of the diseases and pests that are mentioned above, or any other biotic or abiotic stress factors, is an important aspect in providing varieties for multiple growing systems and climates. It is preferred to breed for a combination of resistances to create a variety that is most suitable in a certain situation or environment.
In order to create cucumber varieties that are satisfying the needs of growers and/or consumers, many considerations have to be taken into account. The goal in a breeding program is to combine within a single variety or hybrid an improved combination of desirable traits from the parental germplasm. These traits may include higher yield, field performance, resistance to diseases and insects, and tolerance to drought, cold and heat. Like for most fruit crops, also for cucumber it is apparent that fruit quality is of the utmost importance. Fruit quality includes aspects such as external and internal color, shelf life, fruit size, skin type, firmness, texture, and size of the seed cavity. In addition, characteristics related to optimum plant development are very important for the grower, such as uniformity and speed of germination, growth rate, time to maturity, and plant uniformity. Since many hybrid varieties are gynoecious, bearing only female flowers, the capacity for parthenocarpic fruit set is then also an essential trait.
Cucumber is a diploid plant species with seven pairs of chromosomes. Cultivated cucumber plants have male and female flowers, which can be present together in monoecious plants, but in present-day cultivars commonly gynoecious (all female) plants are used. Cucumbers are easy cross-pollinators but can also self-pollinate when female and male flowers are present in the same plant.
Like in most crops, commercial cucumber cultivars were initially open-pollinated, but nowadays many high yielding hybrid varieties are available, often parthenocarpic. Cucumbers are grown throughout the world, mainly in open field, and are adapted to many different climates and circumstances. As mentioned earlier, many different types are available, and different regions have different preferences in size, fruit type, skin color, etc. Since most cucumber types belong to the same species, limited crossing barriers exist and combinations between types are frequently developed in breeding programs, although certain specific characteristics might be difficult to recombine into a new type.
Early flowering plants that have a good fruit set contribute largely to the potential yield of a pickling crop. Gynoecious flowering in combination with the ability to parthenocarpic fruit set without a large number of aborting fruits provides the growers with the option to use the acreage efficiently. No space is required for plants that have to be used to provide the pollen, and the presence of pollinating insects does not influence the setting of parthenocarpic fruits. A fruit size and type that are fitting the growers' needs plays an important role in choosing a suitable variety.
Growers rely on the presence of resistances to pests and diseases in anticipation of a good cucumber crop. In addition, the presence of resistances requires lower pesticide inputs, which benefits both the expenses for the farmer and the environment.
Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.